Numerous studies indicate fundamental limitations in the human ability to do multiple things at the same time. Recent theories on dual-task processing postulate the involvement of cognitive control processes in the coordination of the processing stream of multiple tasks. The most prominent neuroanatomical structure associated with the control of goal-directed human behavior is the lateral prefrontal cortex (lPFC). It has been show with functional Magnetic Resonance Imaging (fMRI) that the lPFC is also involved in the processing of dual tasks. However, the precise role of the lPFC for the control of dual-task processing and the neural mechanisms of dual-task coordination are still widely unknown. The three fMRI studies presented in this dissertation specify the functional role of the lPFC in interference processing in dual tasks.The results show (1) the generality of lPFC involvement across different types of dual-task situations, (2) the functional neuroanatomical dissociability of different dual-task relevant control process in the lPFC, (3) the role of the interaction of the lPFC with posterior task-relevant brain regions for the control of dual-task processing

Figure 1: The central bottleneck model in the PRP paradigm (Pashler, 1994). Two stimuli (S1, S2) are presented with different temporal overlaps (stimulus onset asynchrony, SOA) and participants are required to respond with two motor responses (R1, R2). The central bottleneck model assumes that at short SOAs response selection (RS) is temporally interrupted in task 2 until task 1 has finished. Stimulus perception (P) and initiation of the motor response (MR) can be processed in parallel in both tasks.

Figure 2: Cytoarchitectonic map by Brodmann (1909). Lateral view. Lateral frontal cortex is colored. red: motor cortex; orange: premotor cortex; blue: prefrontal cortex. Numbers refer to the Brodmann areas. (taken from Barbas, Ghashghaei, Rempel-Clower, & Xiao, 2002). The lateral prefrontal cortex is part the frontal lobes which comprise the most anterior part of the cerebral hemispheres. Identification and classification of subregions within the frontal lobes are based on morphological features like surface landmarks and microscopic analyses of the constituent neurons resulting in cytoarchitectonic maps. The depicted cytoarchitectonic map by Brodmann (1909) is one of the most widely accepted. Three primary functional subregions of the frontal lobes can be identified on the caudal-to-rostral axis of the lateral frontal surface: motor cortex, premotor cortex and prefrontal cortex. In addition, medial frontal cortex has its own subdivisions, interacting strongly with the lateral frontal regions. The primary motor cortex (Brodmann’s area (BA) 4) is the smallest and most homogeneous of these regions, mainly stretching along the central sulcus. Rostral to BA4, the lateral premotor cortex (BA 6) extends along the precentral sulcus and gyrus. Often, BA 8 (frontal eye fields) and BA44 (pars opercularis) are also counted to the lateral premotor cortex. All cortical regions anterior to the premotor cortex are called the prefrontal cortex (PFC). The PFC may be subdivided into several subregions: (1) dorsolateral PFC (dlPFC, BA 9/46), (2) ventrolateral PFC (vlPFC, BA 45/47), (3) anterior PFC (aPFC, BA 10), (4) orbitofrontal Cortex (OFC, BA 11/12/13/14/47), (5) medial PFC (mPFC, BA 24/32). The dlPFC and the vlPFC can be anatomically separated as the neural substrate dorsal and ventral to the inferior frontal sulcus (IFS), respectively. It will be referred to these two subregions stretching along the three frontal gyri (superior, middle and inferior frontal gyrus), when using the term “lateral prefrontal cortex”.

Figure 3: Resuts of Study 2. Whol-brain analysis fort he comparison of dual-task blocks with random order and fixed order (red) and blocks with set sizes of 8 vs. 4 S-R mappings (green) as well as the conjunction of both factors (blue).